Thermotropic liquid crystalline polymers (LCPs) are an important class of polymers, which are generally wholly aromatic molecules containing a variety of heteroatom linkages including ester and/or esteramide linkages. Upon heating to sufficiently high temperature, LCPs melt to form a liquid crystalline melt phase (often referred to as "anisotropic phase") rather than an isotropic melt. Generally, LCPs consist of linear ("rigid rod") molecules that can line up to yield the desired liquid crystalline order. As a result, LCPs feature low melt viscosity and thus improved performance and processabilities.
Because LCPs orient to form "rigid rod" linear molecules, LCPs exhibit extremely high mechanical properties. Thus, it is well known in the art that LCPs can be formed into shaped articles, such as films, rods, pipes, fibers, and various other molded articles. In addition, it is also known in the art that LCPs, particularly in the fiber form, exhibit exceptionally high mechanical properties after a heat treatment process. However, all of the known methods in the art describe formation of only the low denier fibers, e.g., of about 5 deniers per filament (dpf), which exhibit high mechanical properties in their as-spun as well as heat-treated forms. Furthermore, there are no reports in the prior art that filaments having multilobal cross-section can be made from LCPs. More importantly, filaments of LCPs generally do not adhere to various other similar or dissimilar materials.
Numerous patents and publication describe LCPs, method of making LCPs, and the characteristics and uses of such LCPs. Among these are the following, all of whose teachings are incorporated herein by reference:
U.S. Pat. No. 4,183,895 describes a process for treating anisotropic melt forming polymeric products. A process of heat treatment reportedly yielded fibers having enhanced mechanical properties, and the fiber tenacity was reported as being increased by at least 50% and to at least 10 grams per denier.
U.S. Pat. No. 4,468,364 describes a process for extruding thermotropic liquid crystalline polymers (LCPs). It is claimed that extrusion of an LCP through a die orifice having an L/D ratio of less than 2 (preferably 0), and at a draw-down ratio of less than 4 (preferably 1), yields filaments featuring high mechanical properties.
U.S. Pat. No. 4,910,057 describes a highly elongated member of substantially uniform cross-sectional configuration which is capable of improved service as a stiffening support in an optical fiber cable.
U.S. Pat. No. 5,246,776 describes an aramid monofilament and method of making the same.
U.S. Pat. No. 5,427,165 describes a reinforcement assemblage formed at least in part of continuous monofilaments of liquid crystal organic polymer(s). The polymers used therein are primarily aramids.
Japanese laid open Patent No. 4-333616 describes a method of manufacturing filaments of 50 to 2000 dpf from molten liquid crystalline polymers. The heat-treated mechanical properties of these filaments were significantly inferior to the properties reported for the corresponding lower denier filaments of 5 to 10 dpf
J. Rheology 1992, Vol. 36 (p. 1057-1078) reports a study of the rheology and orientation behavior of a thermotropic liquid crystalline polyester using capillary dies of different aspect ratios.
J. Appl. Polym. Sci. 1995, Vol. 55 (p. 1489-1493) reports orientation distribution in extruded rods of a thermotropic liquid crystalline polyesters. The orientation function increases with increasing apparent shear rate from 166 to 270 sec.sup.-1, but decreases with increasing apparent shear rate from 566 to 780 sec.sup.-1.
Although much work has been done and many improvements have been made regarding LCPs, one area in which further improvement is desired is with regard to improving the adhesion characteristics of LCPs to each other and to other materials, for example, to materials made of rubber or having a rubber coating.
Accordingly, it is an object of this invention to provide thermotropic LCP filaments, fibers, yarns and monofilaments, and cords made therefrom, which have improved adhesion characteristics, and in particular to provide LCP filaments, fibers, yarns and monofilaments, and cords made therefrom, having improved adhesion characteristics to rubber and rubber coated materials or substances.
It is a further object of this invention to provide heavy denier LCP filaments, fibers, yarns and monofilaments, and cords made therefrom, having improved adhesion characteristics, and in particular to provide for LCP filaments, fibers, yarns and monofilaments, and cords made therefrom, of greater than about 50 denier which have improved adhesion characteristics to rubber and rubber coated materials.
It is an additional object of this invention to identify substances which can be applied to LCP filaments, fibers, yarns and monofilaments, and cords made therefrom, to improve the adhesion of such filaments, fibers, yarns and monofilaments, and cords made therefrom, to rubber and rubber coated materials.
Another object of this invention is to provide a process for "treating" or "finishing" LCP filaments, fibers, yarns and monofilaments, and cords made therefrom, in order to provide filaments, fibers, yarns and monofilaments, and cords made therefrom, which have improved adhesion characteristics to rubber and rubber coated materials.
Additional embodiments will become apparent to those skilled in the art by means of the specification and examples contained herein.